In flue gas desulfurization (FGD) processes, hydroclones are often used to treat the end sludge by-product of the process. They de-water or concentrate this scrubber sludge just before it is sent to a landfill or otherwise disposed of. Such use reduces the volume of this sludge by-product because any water therein is removed or at least diminished, thereby reducing the cost of its disposal.
Generally, during operation, a hydroclone will separate the incoming product into two separate streams. One will be mostly liquid with little sludge therein while the other will contain mostly sludge with little liquid therein. It has not heretofor been fully realized that this feature of separating an incoming product into two separate streams, along with others, may be quite useful in improving the performance of the upstream flue gas desulfurization process.
In a typical FGD process, incoming combustion flue gas from a boiler, furnace or the like is sprayed with a chemical reagent in a scrubber or absorber tower. This reagent reacts with the sulfur dioxide (or other targeted contaminant) in the flue gas thereby cleansing the flue gas before it is released to the atmosphere. The spent reagent and removed sulfur dioxide collect in the bottom of the scrubber tower where it is subsequently removed and discarded or otherwise disposed of. It is just prior to disposal that hydroclones are oftentimes utilized in order to reduce the volume of this bottoms product sludge.
To increase reagent utilization, FGD processes oftentimes recycle a portion of the bottoms product back to the spray heads directly from the bottom of the scrubber tower so that any un-utilized or under-utilized reagent will be fully consumed before it leaves the tower and is discarded. While this has led to increased performance, the delivery of such bottoms product to the spray header poses an additional problem of maintaining the property of this bottoms product within a certain range. In some cases, the location of the suction exit from the bottom of the tower becomes critical since the bottoms product to be delivered to the spray nozzles must not contain too much sludge nor can it contain too little reagent.
It is thus an object of this invention to provide an FGD process whereby the composition of the returned bottoms product is improved and is known with greater certainty. Another object of this invention is to utilize a hydroclone to further control or maintain the desired consistency of the recycled product. Yet another object of this invention is to increase the use of the recycled bottoms product such that less additives or fresh reagent need be supplied or injected into the FGD process. Still another object of this invention is to enhance or promote the purification of the bottoms product sludge that is sent for disposal. Another object of this invention is to increase the average gypsum crystal size sent for disposal, with less contamination therein, so that subsequent uses can be accomplished. Still another object of this invention is to promote the re-use of crystal fines in the bottoms product for greater removal of sulfur from the flue gas. These and other objects and advantages of this invention will become obvious upon further investigation.